As a practical matter in the past it has been the practice to produce knitted elastic garments such as hosiery from two or more yarns. In other words it was not as a rule possible to knit hosiery from a single yarn. In the knitting of hosiery, therefore, it was common to utilize a yarn which was spun from cotton and/or wool together with a second yarn which had the function of contributing to the hosiery the highest possible degree of elasticity. This is important in the case of stockings since the feet and legs of potential wearers can be greatly different in shape and dimensions. A knitting machine is, however, limited in the dimensions with which the tubular articles are to be knitted. The elastic yarn incorporated in the hosiery, therefore, must assume the function of allowing the garment to accommodate itself to the foot not only at the heel but also at the toe and to the leg all without the formation of folds.
To achieve this, knitted hosiery technology has developed a variety of techniques. Initially textured polyamide was used as a so-called plated yarn to contribute elasticity to the knitted goods. Subsequently elastomers (for example Lycra) entered the market in a significant way and the elastic yarns were so-called wrapped yarns and colored core yarns. The elastomer thread, for example (Lycra) could be wrapped with polyamide or could have cotton thread spun around the elastic core.
In spite of these developments, to date the hosiery structure has not changed materially. Now as then, two yarns are knitted together when the hosiery article is to be elastic. The plating technique has required the knitting yarn and the plating yarn always to maintain desired positions relative to one another. Usually the plating yarn (textured polyamide, wrapped yarn or core yarn) was provided on the inner side of the stocking while the outer side of the stocking was formed by cotton yarn, wool yarn or a blend thereof. The plating technique, however, has created two significant problems for the hosiery knitter.
(a) The two yarns must always be colored exactly the same. In practice this is not possible since no yarn supplier has all of the yarns which may be used for stocking manufacture in its program. Different substrates dye differently. Color deviations between the plating yarn and the knitting yarn are therefore frequently unavoidable.
(b) The plating technique has a defect frequency of 2 to 5% depending upon the nature of the knitting operation and the productivity of the enterprise. This means that 2 to 5% of the stockings have the yarn for the front and back sides interchanged. Since the colors do not match precisely, this means that the stockings will have stripes where the yarns have been reversed in position so that the stockings can only be marketed as second quality goods or cannot be sold at all.
These problems have plagued the industry even prior to the beginning of 1960 when French patent 1,205,976 was published describing the production of socks and men's hosiery by combining a nonelastic and elastic fiber intimately in a spun yarn. The latter yarn, however, had a very high elongatability and was not fully satisfactory as excessive elongatability is also a disadvantage since it is important to provide in such hosiery a certain restoring force upon elastic deformation to ensure a perfect conformity of the hosiery to the foot and leg. The yarn must have excellent appearance when knitted into the article and a pleasing soft hand in the fabric. These features were not characteristic of the earlier yarns.